In the digital broadcast using the satellite and ground waves, data broadcast is in practice as attached to the ordinary audiovisual programs. This makes it possible to provide viewers with interactive services. There are also cases in which the data broadcast alone is provided as independent programs.
FIG. 1 shows the overview of the data broadcast. Contents 2 include a plurality of content elements CE1 to CEn. Each of the content elements CE1 to CEn is provided with a table ID. The same set of content elements (namely the contents 2) are repeatedly broadcasted.
Each contents element is subdivided into a plurality of packets (i.e. packetized) and broadcast. On the receiving device side, the subdivided packets are reorganized to obtain the content elements.
The content element CE1 is described for Example in the HTML language. Therefore, the table ID of an image to be displayed or the table ID of the link location are described.
On the receiving device side, first the content element CE1 is acquired and interpreted, and an image to be used for reference is acquired according to the table ID. However, in the case a content element having the table ID intended to acquire is the one that has been sent already out of a set of content elements, the content element cannot be acquired. However, the same contents 2 are transmitted repeatedly, the content element having the intended table ID can be acquired out of the next set of content elements.
Also in the case an operator of the receiving device chooses and determines the link location by a remote controller or the like, the content element of the link location included in a set of content elements is acquired in the same manner as described above.
The repeated broadcast of a set of content elements as described above makes it possible on the receiving device to perform the process of linking or reference without storing all the content elements.
If the memory capacity on the receiving device side permits, it may also be arranged that all the contents in a set are once stored to perform the process of linking or reference.
Concrete examples of contents for use in the data broadcast will be described using the HTML document shown in FIG. 2. The HTML document can be displayed using the browser application program as shown in FIG. 3. That is to say, the browser application interprets the contents of the HTML document described shown in FIG. 2 and displays the images as shown in FIG. 3.
The lines 201 in FIG. 2 specify the position and the size of an object. At the time of browse-display, the lines 201a for example specify; a position 50 pixels from the left and 300 pixels from the top; and a size of a width of 300 pixels and a height of 500 pixels. The lines 202 in FIG. 2 specify concretely which objects are to be displayed according to the lines 201, and describe the operation when objects are chosen. For example, the lines 202a specify to display an image file in http://www/dirA/001/s1.png (table ID) and are described to display in the vicinity of the image file “This image is in PNG file.”
To restore the above contents using HTML form, the receiving device must acquire a necessary packet out of a stream sent from the broadcast station side in packets (referred to as the transport stream), reorganize the content elements, and further restore content elements of image data and the like that are used for reference.
However, there are many technical standards for the image data and the like, depending on the receiving device, not all the types of image data can be restored. In other words, when a receiving device is not provided with the function (hardware circuit and/or software) for restoring the type of the image data in question, the image data of that type cannot be restored.
In spite of the above situation, the receiving device cannot determine whether or not the image data in question can be restored unless the receiving device acquires the packet, that restores the content elements (See FIG. 2), and acquires the description of the restored content elements (See lines 202a in FIG. 2). That is to say, whether or not the image data can be restored can be determined only after acquiring the extension of the file name of the image data being used for reference.
Depending on the image data, there may be a case in which the data of a different version cannot be restored. In such a case, the extension only cannot determine whether or not the restoration is possible. In such a case, the impossibility of restoration is learned only after the image data are acquired and transferred to the application that performs the restoration. There is also the possibility of an incorrect operation as the case may be.
In any of the above cases, many processes must be performed before it is determined that image data are included that cannot be restored. There is also a problem for example when a process is to be performed in which all or part of contents are not displayed when it is determined that the image data partially includes those that cannot be displayed, the processes up to that determination become useless and also much time is consumed.
The above problems occur also in the case a method is employed in which the processes are performed after a set of content elements are once stored.
There may be also a case in which even if the data can be restored, the data cannot be acquired in the first place because of too large in a size of the data. In such a case too, the processes performed end up in waste.
The present invention has an object of providing a broad cast system that makes it possible to determine easily whether or not the contents can be restored in an early stage of data acquisition in view of the above-mentioned problems.
Another object of the present invention is to provide a broadcast system that makes it possible to determine before acquiring the data whether or not the data can be acquired.